Hardness testing and measuring device



Aug. 14, 1956 R. FUCHS EI'AL 2,758,471

HARDNESS TESTING AND MEASURING DEVICE Filed July 7, 1953 3 Sheets-Sheet2 INVENTORS RICHARD FUCHS OSKAR POSCH ATTORNEY Aug. 14, 1956 Filed July7, 1953 R. FUCHS ET AL 2,758,471

HARDNESS TESTING AND MEASURING DEVICE 3 Sheets-Sheet I5 7 I NVENTORS 103RICHARD wens osmn POSGH "Intent for obtaining reliable results.

United States Patent 'ice 2,758,411 'HAR'DNE'SS TESTING AND MEASURINGDEVIGE iticltata Fu hs, nansbach, westetwla, and osla l gs ch,SdiWabisch Gmund, German nss'ignnt s tfd lcter Fl'ilis ErsteNairosschinirge'lfalii'ik Deu'tschlands, Rahs bach, Westerwald, GermanyApplication July 7, 1953, Serial No. 366,524

priority, application tictman my 10, T1932" 7 16 Claims. (Cl. 73-78)This invention relates to a device the detennihing the ha'fdiless 6f"ceramic ct artificial 'c 't'ifnpdund ni-ate'r'ials. It

'gr'iildihg 'whe'els, bricks, plaster, nce'rs pavcrhen the like, and isof the kind iii which a chisel-shaped tool is adapted to penetrate intothe material to be tested and; simultaneously to perform a reciprccatoryand, preferably, alsoa turning or rotary movement. I V The main objectof the invention is the provision 'of' a handy contrivar'lce orimplement of the described charac tc'r, which may be in the shape, forexample, cf a'hahd drilling machine, a pneumatic hammer, or the like,and can be fixed or suspended from a tripod or other-stand, and by meansof which absolutely reliable readings can be obtained independent of thenature of the material being tested.

Another object of the invention is the provision of a device of thedescribed character Which will permit accu rate determination of thestructural strength of materials of the class referred to, andparticularly of such mafe-fial-s in which the adhesion of the particlesdepends on'the use of synthetic binders of any description.

The solids which are particularly adapted for testing by a device inaccordance with this invention are kit a class which is not so much of abrittle but more of a "tough nature, which involves the risk that thepene'tr-a tion of the chisel into'the material willnotdestroyi-ts'str'ilcture, but will simply dislodge or compress andthereby wedge the particles firmly together.

-A further object of the invention resides in'the employ- 'ment ofparticularly defined materials for the chisel in as much as, besidessteel, other materials may be used, *sueh'as sintered carborundum andother highly resistant materials. Again, the shape or" the chisel is tobe subh as will permit an easy and precise penetration into the materialbeing tested, which is an indispensable require- The shape at thechisel, in accordance with the invention, is such as will the testedmaterial, ofya eircular-pressurearea of large diameter by the combined:p'ounding and turning-"movem'ent of the tool, as such surface wouldbesubjectedpto pressure-only.

preve'nt the formation, in the centre ofthe'drill'hole'of' Another oneof tile moreimportantobjectsoftheinvention is the measuring of the depthto which the ehi-sel penetrates into the material, whichisachievedby-"keeping *mat'eriahit is possible todetermi'ne the workprfd'r fned by' the device in 'eiiecting such pehetratidn, eifid tlfrebytonetcnninc the relative hard ness-bf'the'testedmate a1.

S'till a'ilother'object F is the prm isitin of adevi ce" ccbid'aficewith the ihventidn which shall "be capable *of 2,758,431 Patented Aug.14, 1955 With these and other objects in view the invention consists inthe provision of a hardness testing and measuring deuce having areciprocating and simultaneously revolvir'lg chisel for penetrating intothe material to be tested. The chisel is supported in a holder which iscapable of sliding and turning movement and which constitutes one of 'atleast two mutually connected'movable masses (in a physiclal sense)within a housing, while the other mass may be constituted, for example,by a balance beam-like eohtrivan'e'e. Theinvention, however, alsoincludes the elnpld' hic'nt of "other masses for the purpose, such, forins't-an'ce, as gear parts and others. The connection between thesemasses is preferably devised in such way as to cause them to carry outmutually opposing movements dlihing 'test, which means that, when thechisel penetrates into the material, the mass of the chisel holder willrenew for exam le in a downward direction while at the shine timethe-other mass, for instance the balance beam device, to whichadditional weights may be added, moves tlpwaids. In this way acompensation of the moving rhasss is obtained so that the implement maybe employed in any position desired. It may be attached to a stand so asto act downwardly, or 'heldfin a horizontal position as mig-ht berequired when testing the hardness of wall" at al, or in erted, as forexample in 'the'testing efc'ciling rnaterial'in buildings.

lii'order to advance the chisel'during its combined recipi'bea l aiidrotary-hlovemeht, the invention provides means s itable toimpa'rt to thechisel holder a force in the directionoi penetration of-the chisel.Ifthe contr'ivance, when in use, depends from a tripod or stand, thepenetration p'rodu'ciiig means may be constituted for example by the"weight of the device itself. For use in other working positions, theexample hereinafter described includes a spring arrangement which byreason of it's'particular construction provides avpre'ssure upon thechisel holder in the direction of penetration and that remains uniformduring penetration.

The'above, 'and'other objects, features and advantages 'of theinvention, will be apparent from the accompany- -ing-sheets of drawingswhich illustrate a preferred embodifnentof the invention. It is to'beunderstood, however, that the invention is not intended to be limited'by the eitample shown and'described, but that various alterations tosuit convenience or requirements :may be reso'r ted to without therebydeparting'from the spirit'of the invention.

In the drawings: V

Fig. 1 represents alongitudinal section through a hardness testing andmeasuring device in-accordance with the invention its "working partsbeing shown in perspective. i

Fig. 2 is a detail view-of anassembly included in'the deviceembodyingthe invention, butnot shown on Fig. 1.

Figs. 3 to 5 illustrate the various Working positions of control meansshown in Fig. 1.

Fig. dis a detail of Fig. l onanenlarged scale. Figs; 7--and -8illustrate enlarged representations of two chiselpoints constructed inaccordance with the invention.

Fig. 9 shows'in side elevation a stand for the attachmentthereto of adevice in accordance with "Fig. 1 and of a workpiece to be tested.

Fig l0 isa p'lan view of the device illustrated in 'Fig. 9.

Referring to the drawings in detaiL-and' to Fig. 1 in pan tieular,thedevice embodying this invention includes a housing '12 of elongatedshape which is closedat its'top "by a-lid 14 formed with-a handle 13.Within this housing, in a hub 15, is arranged an electric motor 16 *byat means of which movement is imparted to the various operating parts ofthe device. The motor shaft 17 protrudes vertically from the motor andat its top is arranged to drive an air compressor 18. The air compressor18 i may consist of a rotary pump 26 which is held in a hub 19, and hasrotary blades 21 connected to the shaft 17 at the upper end thereof. Theblades of this air compressor are preferably made of flexible material.

At its bottom end the shaft 17 is provided with a reduced diameterportion 17a to which a pinion 22 secured for rotating the driving ormain shaft 24 of the device through meshing engagement with a gear wheel23 on the latter. The shaft 24 is journaled in the bearings 25 and 26.Fastened to the shaft 24 is an eccentric 27 which is universallyconnected, for example by means of a suitable ball bearing (not shown),to a connecting rod 28. Provided at the free end of this rod 28 is aball socket joint 29 by means of which it is in universal connectionwith a bell crank lever 30. This bell crank lever is arranged to rock ona pivot pin 31 and is connected at its other end by a pin 32 with aforked head 33 which, in turn, is connected by a ball socket joint 34with a tool holder 35.

The pivot pin 31 of the bell crank lever 30 is mounted at one end of abalance beam, which consists of two identical members 36 and 36aarranged at the opposite sides of the bell crank lever 30 and rockablysupported on a shaft 37, which is journaled in bearing arms 38. At theirfree ends the beams 36 and 36a are provided with tabs or pads 39 ofsound absorbing material, such as felt for example, each adapted toslidably cooperate with a guide surface of a related guide wall 40arranged in the housing 12 of the device. Extending upwardly from eachof the free ends of the balance beams 36, 36a is a toothed rack 41 (Fig.2) which will be hereinafter described in detail and which is omittedfrom Fig. '1 so as to avoid confusion with respect to the partillustrated therein.

The tool holder 35, a chisel holder in the present example, is slidablyand rotatably journaled in hub-shaped bearings 42 and 43 Within thehousing 12. Near its upper end, the tool holder 35 is provided with agear wheel 44 which is in engagement with a pinion 45 on the drivingshaft 24, while somewhere about its central portion the tool holdercarries a roller 46 adapted to cooperate with a cut-off switch assemblyfor the driving motor. There is further provided in the housing acounting mechanism 47 which is driven from the main shaft by means of acord and pulley transmission 48. At its lower extremity the tool holder35 is provided with a cap nut 49 for the attachment of a tool, such asthe chisel 50 for example, and said cap nut also serves as a bearing forthe tool holder 35 in the hub 43.

The aforementioned cut-off switch. assembly consists of a switch lever52 which is pivotally mounted on a bracket 51 near the bottom of thehousing and acted upon by a spring 53. At its upper end the lever 52carries a rod 54 for the actuation of the switch which is shown in Fig.6. Movement is imparted to the switch lever 52 by means of a pivotallyarranged locking lever 55. Both the switch lever 52 and the lockinglever 55 are provided with knife-edged abutments 56 and 57, whosemutually cooperating positions are illustrated in Figs. 3 to 5. Thelocking lever 55 is rockably supported on a shaft 58 car ried by anadjusting lever 59 which, in turn, rocks on a pin 61 carried by abracket 60. The arrangement is such that the axis of the pin 61coincides with the edge of the abutment 56 of the lever 52, so that theadjusting lever 59 can be pivoted on its pin 61 about the edge ofabutment 56 by a movement imparted to the arm 62 thereof and the lockinglever 55 will follow such movement. The free end of lever 55 cooperateswith the abutment collar or roller 46 on the tool holder 35. Forstarting the device after a previous automatic stop, a push button orplunger 63 extends through the wall of the housing 12 and has abar-shaped continuation guided in a bearing 64. The inner end of plunger63 is pivotally connected to a bell crank lever 65 which is pivoted onthe switch lever 52 and provided with links 67 which are connected tothe locking lever 55, or the knife-edged abutment 57 thereof. In orderto prevent crowding of the drawings all parts of the above describedcut-off switch assembly are represented only singly, while in practicethey may be duplicated. This more especially refers to the parts 65, 67,55 and 59 which, as already described, are symmetrically positioned inrelation to the switch lever 52.

Referring to Fig. 2 it will be seen that the toothed rack 41 on thebalance beam 36, which has already been referred to, cooperates with atoothed segment 68, which is acted upon to move in a counter-clockwisedirection by a convolute spring 69 so that the balance beam 36 isconstantly subjected to a force tending to move the related end of thebeam downwardly in the direction indicated by the arrow 70. The toothedsegment 68 has the formation of an Archimedean spiral which causes theforce acting in the direction 70 to be of a constantly uniformmagnitude, which means that, as the force exerted by the springincreases or decreases, the moment arm of the segment 68 in mesh withrack 41 varies in the opposite direction so that the downward, springgenerated force on the beam 36 is constant, even though the latter isdisplaced in response to the penetration of the tool 50 into thematerial being tested. It is to be understood that each of the beams 36and 36:: may have a spring loading device associated therewith similarto that described in connection with beam 36.

Fig. 6 illustrates the electric switch which is preferably used in thedevice shown in Fig. l and which comprises the two contact plates 71 and72 fixed to a lug 73 of housing 12 and connected to the leads '74 fromthe motor 16. The switch operating rod 54 which is carried by the switchlever 52 is passed through an aperture 56 in the contact plate 71 andjoined to the contact plate 72 as by means of a rivet 75. Thearrangement of the two contact plates is such that in their electricallyconnected position, as illustrated, the two contacts 77 are closed andthe motor 16 is energized. When the above described cut-ofi switchassembly is operated by means of the collar 46 On the tool holder 35,the connecting bar 54 moves outwardly and the two contacts 77 becomeseparated.

In the hardness measuring and testing device as hereinbefore describedtwo movable masses are coupled to each other so as to wholly or partlycompensate their weight during their movement in order to enable the useof the device in any straight or inclined working position that may berequired. One of these masses (the term mass must here be interpreted tomean weight) is constituted by the reciprocating and rotatable toolholder 35 and the other by the balance beams 36 and 36a, which massesare mutually connected by the forked head 33 and one arm of the bellcrank lever 30. The force by which the tool, during its operation, iscaused to advance in its direction of penetration into the material,

is produced by the weight of the tool holder 35, the spring arrangementsuch as illustrated in Fig. 2, and the beams 36 and 36a. Spacedapertures, such as 79, may be pro vided in the balance beams 36, 36a inwhich additional weights may be applied if this should be required for abetter compensation of the masses.

The eccentric 27 on the driving shaft 24, the connecting rod 28 and thebell crank lever 30, which is connected to the tool holder by the forkedhead 33, constitute the transmission by means of which the rotations ofthe driving shaft 24, are transformed into reciprocating movements ofthe tool holder. The pinion 45 on the driving shaft, which is inengagement with the gear wheel 44 on the tool holder, forms thetransmission by means of which the rotary movement of the driving shaft24 is .transmitted to the toolholder and by means of which the chisel iscaused to -perfdrm a constant rota'ry move- 'rhent; Instead of aco'ntihuo'us rotation it'- is also possible to transfer tb the toolholder-yer to the 1601; an intermittent rotary movement, as bytheintei'position at a suitable place, of a separable clutch, by means'of which the tool may be singularly displaced about it's longiiudihalaxis only when it is disposed either at one end or the "other end Ofitsrecip'rdcatin' 'tr'aveho'r when *it is dispes'ed at each 'of the'o'pp'site ends of its reciprocating travel if the latter shouldbefotihdconvenient.

The mode of operation of the device described and illustrated 'is asfoll'ows: In the QN pcsition of the switch hown in Fig. 6, 'the meter 16nfives "the ihaih shaft-24th16ukhthe -gehis22 arid 23 Thisefte'ct'shdth'a recipro catofy t hverhent of the t561 h'oldr 35, aiid"there- \"tvitliofhhc 661 50, tlii'iigl'i 'tliefiiarts 27 28 and 30, anda'r'otaryrhcverhent ofth'e tobl hblde'r ahd'the tool through the g'ai-s4 1, 4'5. Diiringth'es'e-iii v'enient'st'hecduntihg lilechaiiisih17is-act iiafed by tli'e s ft24, ahiith'e tool is also loa'de'd ahacans-ea gra ally to iieht'ra't into the material to be tested ariii'tbh'tiiiii'e ihlhisdiitactibh hyfthe coiiibihe'd actin Bftlie -35" d hy'the spriiig' inEaiisilliis r t' "-b' se'nt'hat I v blb'clwi'se'ili'rectidh; asyview'eii ih Fig. '1; about their 's'iiiiiiortih'g pivot37, while the hell cra'nk 30 rocks about the pivot pin 31 carried by thebeams. 'Ihus, the be'ai'ns 36 an "361'; donot follow the rocking of thebellc'rank 3h, hiit rat'heract iipwardlyjon lzit'trs "ivot'31'to ray deaconstant downward force if adlo n the tool holtler 3'5. Fii'rthe'r, 'themass "of the "beams 36 and 3'62; is established in relation to the ma'ssof the tool Holder 1 ylbrh ei 1 jbnb t flail 1h l q lie r a 7. ,9' 1 b aa b' sl in pi tto 'tjt e t at older, the react ons ti 'nsmit'ted throughthe sen rahk sharia its illl/6t3j1l0 e earns 3'6fan'd set; arehbstfaht'ially 'cdm'riehsated, she the 'dahifiehing pads 39,fihshdablecohfactfwithjtheguide walls 40, assist ih re isting t ereciprocation r t e beams. s the feel so progressi ely penetrates 'intofthe 'ina'terial being tested, the td'ol holder is feciprbcated betweenlin'iits which a e displaced in thejdownward'directioh, as viewed ih Fi1, ahdthi sacconi ni ed the'ii'r'og'res ve'anglila'r'ihdveij'revioiisly'iioted rn""ed jdep'th. The tif inen'tiation is maintained c'o staiit bythe "fact that 'th'e driviiig'iriotor'blcbrhes aisccnnec ed by theactuat on of the lec't'r'iccu't ofi in a'p'redterniiii'ed position jotthe tool. This wears each time the abtit rniitcio llar sear-me againstthe freeeiid 6f the blocking leyer5 (1 ring thdowiiwafdstrbke' bf thetcol 'hblder. The ijci sition of the lbckin g lever prlior tc th'e'c'fit fiif is siich that the Knife eHQCEabhtYHEnt 57 (Fig. 5)irest'sagaihst 'the edige "80 6f the swrtehiever 52 an'd therebyprevents the movciiient 6f theswi-tch leve in the cut-eff 'clirec'tiohas indicated hy fl'ie threw "81. "If {it 'lhbw occurs, as -alreadyme'htidned, that the lockin "lever 55 is 'cm'ried by "theabutrnentcollar ofthe tool holder about 'its axis 58 'in a counter clockwisedirection, the knife-edged abutmerits? will'he-raised nnt'ilits edgebecomes flush with'the edge of the abutmentiti'offi'theswitchlever'fl(Fig. 3'). The switch l'vrrfiz is 'now free "-to "be immediately moved{in the, direction ihdi'cat'ed by the arrow 8lyby -fneans :Qf its spring53 and thereby opens th'e switch contact 77 75 I6 I "(Fig. 6)to'inferrupt the'iissociated ciiciiit. The :poi'tion of the partsWiIljnOW 'b'e' as shownin Fig.4; and the limitation-of the rockihginovenie'rit of the locking lever 55 'is "effected byhtan's of a furtherabutment '82 on the switch lever 52. i

In order tos'et thedeviceforany desired-depth ofbenetratioirof the'tool,the locking lever 55 ihay 'be turned about its axis 61 upwardly ordownwardly and ti) aiiy exteiitr'eqiiired by means of the adjustinglever "59. Fbr this purpose the device is provided with suitableadjusting means which are not shown'ihthe'drawihg's. 'Th'ese'meahs may,fer instance, include "an adjus'tifig screw s indle, ah eccentric, leveror the like, in connection with the arm'fiz of the lever 59.

For resfettih the 'cut bif sWitch-asse'itibly, the lnfi'ger 63 ispressed into the housing '12:, whieh rnovemehtbf the plu'nger at firstturns thesvv'itch lever 52 t hrdtigh the actidnof the hell crank lever;65, in the opposite dif'ctio ii cf the arrow 81, whereby the p shbwn inFig. -'3 is reestablished. Upon "further 'deprs at the @lfiiigrfifi;since the niovihefii of the lever "52 is lifrii't'ed by the step 83; the'liiik 67 is riow moved downwardly by a rocking moveiii'en't 6f the bell'rank lever '65 "therewith, thelccking lever, 'or the kiii'fe 'edgd abut'e'nt 57, is returned into thef'pos' i1 cf Fig. 5. Files tch is heat intheON-positioh 'ahd the device cdiiiihence's'tb'w k.

Y has eiialriirile. makes it 'possible 0* his?) eihplo'y *fa'c' of the hl o'il'l'e th'ansieel', I y y s'iiitr ed Cai borundum drfth'e like,which are "p os sessim 6f heh'erweamg "prcpcrtis than steel. 'Afii'rthehadvahtage'rests in that the-chisel can be most essiiy'se'e edin 'the t'o'ol holder, nd ihis c'ciiidi'tionfis 'al'rnbstnclisia'er'isahle if hceur'hte hhd c'cifisistent results are t0'bebbtainetl. x

Ahotlierloi hfatibh Hf 'fhe'chisel ehd'is shown in Fi'g. 8, in WlllC themay 34 "of the chisel is {Else at cylindr cal shaiie with flattenedraces 86. The 'faces; this case; are. chanifere'd at ah iang'le f erablyabo'iitkljj to 60; in tl'ii's'way facettes 87 are tarmeaen -the pbund Iface at the free end of the tool so that the lattei nftav be "keptextremely n' "raw (0Z2 torekamhl), This as at ih'thiswa ytli'ecent'ralci'rcular a in the estjgiieshb; ed tb cbti'tinuou siioundingdtiri rotation of the i661 is hel d t5 a rhiniiiiurn diarht anarea would mainly B e-sub eteatb'pressure"w grain of t'lie -silbsfancebeihg 'b'i'okh up asjsh'ou ease. Such a will -e Be tinder cod,chi-fiespoiid's in I it's diarrietc'r ab'pfdkimatly to the width ofchisel. lfifibwithe chisel is cciisfructed iii the'inanhera'siliiistratedih Pig, '8, "siich pressure 'areawill have "g:- li'gihie"ciiar n'etr. On the contrary, the whelefst'ri'lctu'r'e of thegrai'ri'ih the ora- 'iigse'c'tidnof the-chisel Twill becoine broken u's'i'nc circular area i'so'f relatively small "di'ain'eter. Sb itbds'sible, in manner described, to obt': in cdihiiarahle values for theva'i'idus inater'ials-tobe tested.

As already describedjthe device inacc'ordance with invention may also behead "in ccnnctio'n with a stand, of which an example is'shown in Figs.IO- and 1 Lin which the testing and measuring device 11a is rem'ovablysuspended from an arm 100 extending 'from'a column 101'. The arm N0 isvertically 'displac'eable on the c'olurnnilll and may be locked inposition by a screw 102. The'olmm 101 is fastened in a socket 1021?,while "a displaceable carrier supports the object to be tested; forexample-7a grindingwheel1W3. The carrier, for this purpose, is firet- 7erably composed of three star'like arranged arms 104, 105 and 106, ofwhich the arm 104 is telescopically slidable in an opening of the socket102a, while the other two arms 105 and 106 are provided with casters107, by means of which they may run on a plate or table at the top ofthe stand. At the center of the carrier a pin 108 is provided for thereception, or centering, of the grind wheel 103. The latter may besupported, at one side, on a pressure plate 109 of the socket 102a inthe vicinity of the hardness testing device 12a, and at the other sideon rollers 110 arranged on the arms 105 and 106. The rollers 110facilitate turning of the grinding wheel so that the latter may betested at several places on a circle which is concentric to the axis ofthe wheel.

The compressor 18 driven by the motor shaft 17 which has been mentionedin connection with Fig. 1 of the drawings, draws air from outside thehousing 12 through the opening 111 in the latter, compresses it andforces the compressed air through the housing and the clearance, or

a slot, between the bearing 43 and the guide 49 of the tool holder toblow away the chiselling dust and thereby prevent the entry of such dustinto the housing of the device.

What we claim is:

l. A hardness testing device for ceramic and artificially compoundedmaterials comprising a tool holder movable longitudinally and rotatableabout its longitudinal axis, a tool carried by said holder forpenetration into the material to be tested, an electric driving motor,an electric circuit for energizing said motor, transmission means drivenby said motor efiecting rotation of said holder about its longitudinalaxis and simultaneously efiecting longitudinal reciprocation of saidholder through a stroke of predetermined length, loading meanscontinuously applying a load to said holder in the direction of thepenetration of said tool into the material being tested so that, as saidholder is rotated'and reciprocated, said tool penetrates into thematerial being tested, means for damping vibrations transmitted to saidloading means, normally closed switch means interposed in said circuit,and switch operating means opening said switch means automatically inresponse to a predetermined penetration of said tool intothe materialbeing tested to then halt the operation of said motor.

2. A hardness testing device according to claim 1; further comprisingmeans for indicating the revolutions and strokes of said holder prior tothe opening of said switch means so that the relative work required toeifect the predetermined penetration of the material being tested can becalculated.

3. A hardness testing device according to claim 1; wherein said loadingmeans includesa scale balance-like device which is independent of themotion of said transmission means and which applies a constant load tosaid holder in said direction of penetration of the tool.

4. A hardness testing device according to claim 1; wherein saidtransmission means includes a drive shaft driven from said motor, aneccentric on said drive shaft, a bellcrank lever connected at one end tosaid tool holder, a connecting rod extending from said eccentric forconverting the rotation of said drive shaft into a reciprocatingmovement, and universal connecting means between said rod and the otherend of said bell-crank lever; and wherein said loading means includes atleast one balance beam mounted on a fixed pivot, said bell-crank leverbeing rockably mounted on said balance beam adjacent one end of thelatter, and means urging said balance beam to swing about its fixedpivot in the direction applying said load to the holder through saidbell-crank lever.

5. A hardness testing device according to claim 4; wherein said meansurging the balance beam to swing about its fixed pivot includes weightsremovably secured on said balance beam.

6. A hardness testing device according to claim 4; wherein saidvibration damping means includes a fixed guide wall extending, parallelto the plane of swinging of said balance beam about its fixed pivot, andat least one member having a high coefficient of friction mounted onsaid balance beam and slidably engaging said guide wall.

7. A hardness testing device according to claim 4; wherein said meansurging the balance beam to swing about its fixed pivot includes aspring, and coupling means between said spring and balance beamoperative to apply a continuous spring generated force to the balancebeam as the latter is angularly displaced about its fixed pivot duringpenetration of the tool into the material being tested.

8. A hardness testing device according to claim 7; wherein said couplingmeans includes a toothed rack on said balance beam, and a toothedsegment meshing with said rack and angularly urged in one direction bysaid spring, said toothed segment being in the form of an Archimedeanspiral so that, as said spring relaxes in accordance with the angulardisplacement of said segment, the moment arm of the force applied tosaid rack increases thereby to maintain the spring generated forceapplied to said balance beam at a constant value.

9. A hardness testing device according to claim 1; wherein said toolincludes a cylindrical shank secured in said holder, the free endportion of said shank having flattened surfaces at the opposite sidesthereof to define an operating end of substantially rectangularcrosssection.

10. A hardness testing device according to claim 9; wherein the freeends of said flattened surfaces are bevelled at an angle ofapproximately 45 to 60 thereby to further decrease the width of saidoperating end of the tool.

11. A hardness testing device according to claim 1; wherein said switchmeans includes normally engaged switch contacts, and said switchoperating means includes a rockable switch lever, means connected tosaid switch lever and operative to separate said contacts in response torocking of said switch lever in a contact opening direction, springmeans yieldably urging said switch lever in said contact openingdirection, a pivotally mounted locking lever, an abutment on said toolholder engageable with said locking lever when said tool has penetratedinto the material being tested to said predetermined extent to then rocksaid locking lever in one direction, and co operating knife-edgedabutments on said locking lever and switch lever to normally preventrocking of the latter in the contact opening direction, said cooperatingabutments being disengaged by rocking of said locking lever in said onedirection thereby to free said switch lever for opening of saidcontacts.

12. A hardness testing device according to claim 11; wherein said switchoperating means further includes a supporting bell-crank lever, meanspivotally carrying said supporting bell-crank lever for rocking about anaxis coinciding with the knife-edged abutment on said switch lever whenthe latter is rocked in said contact opening direction, and means forangularly adjusting said supporting bell-crank lever about said axis ofthe latter, said locking lever being pivotally mounted on saidsupporting bell-crank lever for rocking relative to the latter about anaxis displaced from said knife-edged abutment on the locking lever andthe path of said abutment on the tool holder so that angular adjustmentof said supporting bell-crank lever serves to vary the extent ofpenetration of the tool into the material being tested that is necessaryto open said switch contacts.

13. A hardness testing device according to claim 12; wherein said switchoperating means further includes a manually operable plunger forrestoring said switch lever and locking lever to the normal positionsthereof corresponding to the engaged condition of said contacts, arockable bell-crank pivotally mounted on said switch lever and connectedto said plunger, and links pivotally connecting said bell-crank to saidlocking lever so that movement of said plunger in one direction firstrocks said switch lever in the direction opposed by said spring and thenrocks said locking lever to again engage said knifeedged abutments onthe locking and switch levers.

14. A hardness testing device according to claim 1; further comprising ahousing from which said tool projects, a stand, means for detachablyconnecting said housing to the stand, a work-piece holder, and means forslidably and turnably mounting said work-piece holder on said stand.

15. A hardness testing device according to claim 1; further comprising ahousing from which said tool projects, and a stand including anupstanding column on which said housing is adjustably mounted, a carrierhaving star-like arranged arms one of which is adjustably slidablethrough the base of said column, a support plate for the material to betested disposed on said base under 5 upwardly from the junction of saidarms.

References Cited in the file of this patent UNITED STATES PATENTS1,283,362 Tone Oct. 29, 1918 1,681,070 Uschmann Aug. 14, 1928 1,902,765Deitsch Mar. 21, 1933 1,991,238 Willey Feb. 12, 1935 2,054,787 Beaverset a1. Sept. 22, 1936 2,330,578 Harris Sept. 28, 1943 FOREIGN PATENTSGermany Dec. 4,

1. A HARDNESS TESTING DEVICE FOR CERAMIC AND ARTIFICIALLY COMPOUNDEDMATERIALS COMPRISING A TOOL HOLDER MOVABLE LONGITUDINALLY AND ROTATABLEABOUT ITS LONGITUDINAL AXIS, A TOOL CARRIED BY SAID HOLDER FORPENETRATION INTO THE MATERIAL TO BE TESTED, AN ELECTRIC DRIVING MOTOR,AN ELECTRIC CIRCUIT FOR ENERGIZING SAID MOTOR, TRANSMISSION MEANS DRIVENBY SAID MOTOR EFFECTING ROTATION OF SAID HOLDER ABOUT ITS LONGITUDINALAXIS AND SIMULTANEOUSLY EFFECTING LONGITUDINAL RECIPROCATION OF SAIDHOLDER THROUGH A STROKE OF PREDETERMINED LENGTH, LOADING MEANSCONTINUOUSLY APPLYING A LOAD TO SAID HOLDER IN THE DIRECTION OF THEPENETRATION OF SAID TOOL INTO THE MATERIAL BEING TESTED SO THAT, AS SAIDHOLDER IS ROTATED AND RECIPROCATED, SAID TOOL PENETRATES INTO THEMATERIAL BEING TESTED, MEANS FOR DAMPING VIBRATIONS TRANSMITTED TO SAIDLOADING MEANS, NORMALLY CLOSED SWITCH MEANS INTERPOSED IN SAID CIRCUIT,AND SWITCH OPERATING MEANS OPENING SAID SWITCH MEANS AUTOMATICALLY INRESPONSE TO A PREDETERMINED PENETRATION OF SAID TOOL INTO THE MATERIALBEING TESTED TO THEN HALT THE OPERATION OF SAID MOTOR.